Resin coated single fibers for molding compositions



aA. BENSON Sept. 24, 1968 RESIN COATED SINGLE FIBERS FOR MOLDINGCOMPOSITIONS Filed March 9. 1966 United States Patent O 3,403,069 RESINCOATED SINGLE FIBERS FOR MOLDING COMPOSITIONS Burton A. Benson,Richfield, Minn., assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn., a corporation of Delaware Continuation-impartof application Ser. No. 788,461,

`Ian. 22, 1959. This application Mar. 9, 1966, Ser.

4 Claims. (Cl. 161-170) ABSTRACT OF THE DISCLOSURE Filament-reinforcedmolding composition comprising a mass of scattered, discrete, fiat,resin-coated, mono-yam and multi-yarn ber segments. The fiber segments,which are generally between about 1A; and 2 inches in length, are formedby arranging continuous yarns in .a compact single-layer web, coatingthe web with a thermosetting organic resin composition, bringing theresin to a tack-free, brittle state, and then chopping the web.

This application is a continuation-in-part of copending application S.N.788,461, filed Jan. 22, 1959, and now abandoned, which was itself acontinuation-in-part of copending application S.N. 714,856 led Feb. 12,19518, and now abandoned.

Resin moldings reinforced with fibrous glass have recently lattainedconsiderable commercial stature by virtue of, among other qualities,their light Weight, high impact resistance, high strength, and goodresistance to weathering and to the action of chemicals. Since thetensile strength of the fibrous glass reinforcement greatly exceeds thatof the resin, maximum tensile strength is normally attained with a highpercentage of glass. However, sufficient resin must be employed toinsure against voids in the molding, since areas with voids are muchinferior in strength and durability to areas fully impregnated withresin.

The highest strength reinforced resin products presently being marketedare laminates of essentially continuous bundles of ine glassmonolaments, either woven as a fabric or in non-woven lineal alignment.While these products have exceeding high strength in the plane oflamination, their strength in directions through the laminate is usuallyless than 1/30 of that in the plane of lamination. Also, to build areinforced resin laminate of variable thickness, it is diicult to attaingood strength, since it may be necessary to lay up the brousreinforcement in a patchwork manner. lf portions of the laminate aremachined away, some areas my be weakened considerably, if the filamentsreinforcing such areas do not extend into the main body of the laminate.

For uses requiring more uniform strength in three dimensions, strands offibrous glass may be randomly ntermingled and impregnated with resin. Anumber of useful techniques were known prior to this invention, but eachyielded products much inferior in strength and uniformity to theabove-discussed resin laminates.

The inventor has now devised a reinforced resin molding compositionwhich is -characterized by excellent flow ability and by theextraordinary strength and uniformity of the novel molded and curedproducts obtained therewith. Flexural, tensile and compressive strengthsof such molded products compare favorably to strength measurements inthe plane of Ilamination of the strongest resin-impregnated laminates.For example, molded objects made from preferred molding compositions ofthis invention exhibit flexural and tensile strengths of more than40,000 and 20,000 pounds/square inch and up to 90,000 and 40,000pounds/square inch Iand more,

respectively. Moreover, the novel molded products approach isotropy inthree dimensions.

By virtue of its excellent flowability, the novel molding compositionmay be injected under suitable conditions into a matched die set. Thiscapability makes possible, for the first time, large-scale, economicalproduction of high-strength plastic pipe fittings, which heretofore haveusually been laboriously built around forms with pieces ofresin-impregnated glass fabric and lengths of glass yarn. The novelmolding composition is also well suited fo ruse in preforming apparatus.In such use, it provides for the rst time, to the inventors knowledge,preformed products of controlled resin-glass proportion, and by its use,the fabrication of reinforced resin molded products in such apparatus issubstantially simplified.

Briey, the reinforced resin molding composition of this inventioncomprises a mass of loose fiber segments, each fiber segment in turncomprising at least one resincoated threadlike fiber of reinforcement.Typically, each fiber of reinforcement consists of a group of manyhunched, essentially-parallel glass monoiilaments such as a strand,yarn, or roving of monotilaments, each of the monoiilaments having adiameter between about 0.0002 and 0.0006 inch and having aresin-receptive surface treatment. Each of said ber segments is coatedwith strongly-adherent, tack-free resin in an amount of -about 35-60percent of the total volume of the resin-Coated f1- ber segment. Each ofthe resin-coated segments has a length of about 1/32 to 3 inches and acircumference on an average not more than 0.05 inch. To achieve the highstrength products desired, the resins used in the molding compositionsof the invention should have tensile, flexural, and compressivestrengths of at least about 5,000 pounds/square inch, and preferablymore than 8,000, 15,000, and 20,000 pounds/square inch respectively. Theresin on initial heating in bulk to the molding temperature attains aviscosity of about 50,000-5,000,000 centiposes. When the novel moldingcomposition is heated t0 this temperature and is then injected underpressure into a steel mold, the resin does not appreciably flow aheadbut remains with the resin-coated fiber segments so that each movessmoothly, lubricated and cushioned by its highly viscous resin-coating.The resin then hardens to a dense, tough, tack-free and preferablythermoset state.

In a preferred embodiment of the invention, groups or bundles of 204continuous glass monotilaments, each about 0.00038 inch in diameter, arecoated with a latent, thermosetting resin composition and subsequentlychopped to provide a mass of loose, individual, resincoated fibersegments averaging about 0.019 inch in circumference each. By a latentthermosetting resin, is meant a resin which remains fusible andheat-curable after prolonged storage at ambient temperatures but whichon heating cures readily to an essentially infusible and insolublestate.

Although the novel mol-ding composition may be produced by applyingresin to a single bundle of glass filaments by one of a number of knowntechniques and then chopping the bundle into short segments after firstadvancing t-he resin to a tack-free state, such a process is unduly slowand cost-ly. To apply resin simultaneously to a plurality of parallel,widely-space bundles of filaments is likewise wasteful of time andequipment and is not preferred. Instead, it is preferred to combine intoa fiat, compact, single-layered web and in lineal alignment a pluralityof twisted bundles of continuous glass filaments, each of 0.002-0.0006inch diameter and having a resin-receptive surface treatment. This webis passed under even tension through a path of liquid resin compositionwhich is preferably maintained within the viscosity range of 200- 12,000centipoises. Upon removal from the bath, the resin is advanced to anonmal'ly tack-free state, often by simply cooling the resin to ambienttemperature, whereupon the web usually spontaneously separates intoindividual resin-coated bundles. The web is then chopped t lengths of%,2 to 3 inches to provide a mass of loose resin-coated fiber segments.The fibrous reinforcement, after this coating and chopping process,remains essentially linear and unexcoriated.

Although it is preferred that each fiber segment be completely separatefrom other segments in the novel lmolding composition, a few bundles offilaments invariably cohere, but usually they are so lightly bonded toeach other that they tend to separate in normal usage. On rare occasion,when produced by the preferred novel technique just described, a largeproportion of the fiber segments appear to cohere to other segments forno accountable reason. Because of the superticiality of bond, theseseeming aggregates of fiber segments readily separate upon moderateagitation into individual fiber segments, each including a single bundleof 204 monofilaments. Accordingly, an individual fiber segment, as thisterm is used in this description, is meant to apply to each strand intowhich an aggregate of fibers breaks up under agitation, as by turbulentair, of less severity than might fracture the filaments or causesubstantial quantities of resin to flake away from the fibrous matter.Any individual raggregate which does not so break up is also consideredto be an individual fiber segment, even though it be several times aslange as most fiber segments of the molding composition.

It follows from the nature of the coating process that the individualfibers of reinforcement in an aggregate, that is, the individual groupsof bunched monofilaments, are substantially parallel to or lineallyaligned with, and typically spaced from, one another inshoulder-to-shoulder relation. As noted above, they should be onlylightly adhered to one another by the resin coating so that they tend toseparate under normal usage, especially in the mold. However, theindividual groups of monofilaments should remain substantially integra-land form individual, separated, strong fibers of reinforcement. As aresult of this separation, the molding compositions of this inventionform in the mold a continuous resin binder matrix filled essentiallyuniformly throughout with randomly intermingled fibrous reinforcement,and then harden, either by curing or cooling, as a monolithic objecthaving higth strength properties in all directions. It will beunderstood that because of the light adhesion between adjacent coatedfibers the chopping operation breaks the coated web into fiber segmentsof no more than a few fibers. It should be noted that whether the fibersegments have undergone sufficient agitation to be broken into smallersegments is not as important as their susceptibility to separation intoindividual integral fibers of reinforcement in the mold. On the otherhand, the better separated the individual fibers of reinforcement arebefore they are charged to the mold, the better will be the results, andif the adjacent fibers are so strongly bonded together, as discussedhereinafter, that fiber segments of large size resist furtherseparation, strengths will be reduced.

If most of the bundles of filaments are to separate after coating by theabove-described novel process into individual resin-coated fibersegments, it is necessary that the filament bundles or ends (by whichterm they are :generally known in the industry) be at least lightlytwisted. For example, one twist per inch provides good separationwhereas lonly one twist in 18 inches is insufficient. No glass yarn orroving is available commercially at the date of filing this applicationat a twist intermediate these two degrees of twist, but it is believedthat almost one twist per inch is necessary to good separation. Morehighly twisted yarn is also available and separates readily into fibersegments, each of only about one yarn or bundle of filaments. However,it is preferred for this invention that twisting be held to the minimumat which good fiber separation is realized, since this makes easier theimpregnation with resin of the interstices between the monofilaments,whereby stronger molded products may be obtained. If the novel moldingcomposition is produced b-y other than the above-described novelprocess, the filament bundles need not be twisted, except as necessaryto provide sufficient integrity to allow handling without excessivebreakage in the particular resin-coating technique used.

If application of the resin composition to the filament bundles is madeby drawing a web of bundles through a liquid resin bath, the viscosityof lthe bath at the coating temperature should be within the range of20D-12,000 centipoises, as determined with a Brookfield viscometer, andpreferably not above 4000 centipoises. At viscosities much greater than4000 centipoises, it is difiicul-t to hold the resin content in thepreferred range of 50% :or less by volume unless volatile solvent ispresent in the resin bath. Also, the resin less effectively penetratesthe interstices between the filaments. Below about 200 centipoises, theresin composition tends to run off the filaments.

Resins are preferably coated from solution so that the resin willpenetrate the fiber of reinforcement better before soldifying. Further,when resins are coated from solution, a greater latitude is possible inthe choice of the resin, especially in the case of resins that have atendency to cure with heat. Thermosetting resins, after being coated onthe strand, are typically advanced in cure, as by passage under heatinglamps or over a heated drum, to bring them to the desired state ofviscosity under molding conditio-ns.

The viscosity of the bath is readily adjusted by adding solvent or bychanging the temperature, with due regard to the importance of avoidingpremature curing of the resin in the bath. Normally, the viscosityshould remain within the preferred range of 20G-4000 centipoises for atleast two hours without the addition of fresh resin, if waste is to beavoided. However, by replacing resin taken up by the filament bundleswith fresh resin, the pot life is effectively increased, assuming thebath is free from stagnant areas so that the motion of the web ofbundles thoroughly stirs the bath.

The proportion of resin is effectively controlled by passing theresin-coated filament bundles through a calender, with allowance forsubsequent evaporation of solvents, if such are present. If theproportion of resin is more than 60 percent of the total volume, afterevaporation of any volatile solvent, adjacent bundles of filaments tendto cohere if held in shoulder-to-shoulder relationship, resulting inundesirably large fiber segments.

The squeezing action of calender rolls assists in saturating each bundleof filaments by forcing resin into interstices still existing betweenmonofilaments and also assists in providing complete wetting of theglass surfaces by the resin so that adequate anchorage is obtained.Heating of the glass just prior to entering the bath, as by radiantheaters, may also improve bonding between the resin and glass. Filamentswhich have previously been treated with lubricants or other agents whichinterfere with resin anchorage may be cleaned by such action, or mayfirst be washed free of such surface treatment in an appropriate solventbath and the residual solvent removed by heating as just described.Preferably the glass filaments are treated with priming compositionssuch as silane chemicals or organo-metallic complexes to provide evenbetter bonding of resin to glass.

It has been found that molded products of compositions, the individualfiber segments of which substantially exceed 0.05 inch in averagecircumference, have much lower strength than compositions comprisingresin-coated segments of less than 0.05 inch circumference. Thediminution in strength resulting from the use of such larger fibersegments is accompanied by a corresponding loss in uniformity ofstrength and toughness. For example, if an average of more than aboutthree or four resin-coated bundles, each of which contains 204 of the0.00038-inch filaments, cohere in shoulder-to-shoulder relationship andresist separation upon chopping and subsequent moderate agitation, theproducts of such molding compound would be deficient in strength anduniformity.

The above-described novel process has been employed to produceresin-coated fiber segments averaging only 0.006 inch in circumference,and products molded therewith exhibited excellent strength. However, dueto difficulty in handling the web of fragile filament bundles in makingthe molding composition, it is considered to be commercially impracticalto attempt to manufacture resincoated fiber segments averaging less thanabout 0.01 inch circumference, and it is only because the filaments ofthe bundles are continuous (in contrast to staple fibers) that such fineresin-coated fiber segments can be produced by the above-described novelprocess.

Resin-coated fiber segments coming within the approximate limit of V32and 4 inches in length have been used to provide molding compositions inthe practice of this invention. Resin-coated segments of 4-inch lengthWere found to lack fiowability whereas fibers of 2-3 inches or less Wereadequate in this respect for most purposes. Since the strength ofproducts molded from resin-coated fiber segments of 2-inch length are asstrong as those obtainable with longer segments, no sound basis forusing longer ber segments exists. Shorter liber segments are moreflowable, but tests with fiat molded panels indicate some reduction instrength results. A decrease from one to 1/2 inch in fiber-segmentlength is accompanied by a strength reduction of about -15 percent, andabout the same reduction is experienced in decreasing from l/2 to 1Ainch. At fiber-segment lengths below 1A inch, the decrease in strengthis much more significant.

In spite of decreased strength exhibited by fiat molded panels, it isoften preferred to use very short fiber segments to form highly complexparts, taking advantage of the ability of the short segments to flowthrough tiny passages and into small crevices. For many such parts,fiber segments of 1A inch or less outperform longer segments in point ofstrength of finished product, even though the product molded from thelonger segments appears to be homogeneous. This is 'believed to be dueto more random orientation and better interlocking of the shorter fibersegments in constricted areas. For applications wherein improved resultsare attained with short fiber segments, even better interlocking isapparently attained if the fiber segments have smaller averagecircumference.

The novel molding composition exhibits optimum flowability when heatedto a temperature at which the resin coating of the fiber segments has aviscosity of about 100,000 to 500,000 centipoises as measured in bulkwith a Brookfield viscometer. At temperaturs at which the resinviscosity is less than about 50,000 centipoises, the resin tends to flowahead of the fibers. At viscosities above about 5,000,000 centipoises,it may be necessary to use greater pressure to cause the moldingcomposition to ow than is available with a particular piece of moldingequipment. However, it may be preferred in certain situations to utilizemolding temperatures at which the resin viscosity is even higher than5,000,000 centipoises, especially if Very high pressure is required toforce the molding composition into small pockets, since even lesstendency exists at such high resin viscosity for the resin to liow aheadof the fiber segments.

Once the resin-coated liber segments have completely filled a mold, itmay be desired to increase the temperature to speed the cure and toreduce the viscosity of the resin so that a good deal of resin leavesthe mold as a flash, whereby a product of increased glass proportion andconsequently increased strength is attained. The pressure may besimultaneously increased to implement such resin flow, but care shouldbe exerted in forming thin panels to avoid crushing of the glass.Pressure of 7000 pounds per square inch have been applied during thecuring of bulky parts without apparent injury to the glass filaments butpressures of this order are not recommended for molding thin panels. Formost parts, molding pressures fall within the range of 300-5000 poundsper square inch depending -on the shape and complexity of the part. Ingeneral, useful molding temperatures lie within the range of Z50-450 F.,and resins used in compositions of this invention should flow, but notbe too low in viscosity to flow ahead of the reinforcement fibers, at arange of temperatures within this broad range. If the resin isthermoplastic, the die set is normally quenched as soon as a denseproduct is obtained, and the molded product is ejected when solidified.

To insure that the molded product is void-free the resin must besubstantially free from elements which volatize in normal usage. Thepresence of voids in the product seriously detracts from its strengthand deleteriously affects other qualities of the product in specificapplications.

If the resin content of the novel composition exceeds about 60 percentof the total volume, products molded therewith often have resin-rich andconsequently weak areas, particularly if the viscosity of the resin isallowed to drop below 50,000 centipoises before the mold cavity isfilled to the complete elimination of voids. Moreover, strengths falloff greatly at further increase in proportion of resin. The danger ofencountering resin-rich areas is particularly great for complex moldcavities, and in such use, reduction in resin content to about 50percent of the total volume is preferred. Below about 35 percent resinby volume, it is difficult to obtain void-free products.

To allow the fiber segments to be intermingled in random fashion, theirresin coating must be tack-free -at normal temperatures. However, if itis feasible to maintain the molding composition under refrigeration, itis only necessary that the resin -coating be tack-free under theconditions of refrigeration. By refrigerating the molding composition, athermosetting resin which is not considered to be a latent type may beutilized for applications requiring storage of the molding compositionprior to converting it into molded products.

A better understanding of the invention and the uses to which the novelmolding composition may be put may be gained by reference to the drawingin which:

FIGURE l is a schematic View in elevation of a preferred apparatus formaking the novel molding composition;

FIGURE 2 is a schematic View in elevation of apparatus for makingconformable, curable reinforced resin sheet material out of the novelmolding composition'. and

FIGURE 3 is an elevation, partly in section, of apparatus for producingreinforced resin pipe couplings from the novel molding composition.

Referring first to FIGURE 1, a supply of fibrous glass is made availableby a bank of spools 7. Each of the spools contains five ends or bundlesof 204 lightly twisted glass monofilaments, each of which monofilamentsis about 0.00038 inch in diameter. The monolaments are provided with athin size coating which serves to improve the adherence of resin to theglass.

The five ends on each of the spools 7 are free from intertwining and somay be maintained in non-overlapping shoulder-to-shoulder relationshipto provide a wide web, after 'being drawn through an eyelet board 8,past a pair of spaced idler rolls 9 and through a comb 10. The latter,together with a comb 11, serves to space each end equally from the nextat a density of 70 ends per inch. This single-layered web is drawnacross an idler roll 12, into a bath of resin 13, and around acylindrical roll 14, which is adjusted to carry the web of ends close tothe bottom of the bath. The positioning of roll 14 insures that thecontents of the resin bath 13 remain fresh. Suitable means (not shown)are provided for maintaining the resin bath 13 at .a constant level andfor heating the resin to maintain it at a suitable viscosity.

The resin-coated web 15 drawn from the bath 13 is passed between twodriven steam-heated rolls 16, 17 which serve to smooth the resin coatingand to remove excess resin, which forms a bead 18 at the nip of therolls 16, 17. The rolls 16, 17 are adjustably spaced to provide adesired proportion of resin in the web 15. The web 15 then joins anendless belt 19, which may be faced with silicone rubber or other toughlow-adhesion surface such as polytetrauoroethylene film. The belt 19 ischilled by moving in contact with a refrigerated driver roll 20 and coldpans 21. The idler roll 22, around which the belt 19 is also entrained,need not be refrigerated since the other cooling means are adequate toharden quickly the resin coating to a non-tacky state. Hardening of theresin is accompanied by spontaneous separation of almost every one ofthe resin-coated ends from adjacent ends.

The web 15, which now comprises a bank of loose resin-coated ends, isfinally drawn past an idler roll 23 and is gripped lightly by a pair ofdriven rolls 24, 25 to carry it into a conventional adjustable choppingdevice 26. Each of the `rolls 23, 24 and 25 is preferably faced withsilicone rubber. The bed knife 27 of chopping device 26 is preferablymaintained at about 5 C., since the bed knife may collect resin if at ahigher temperature. The action of chopping device 26 assists in breakingthe ends apart to provide individual resin-coated fiber segments 28. Toafford optimum intermingling of the novel molding composition made up ofthe fiber segments 28, it may be preferred to agitate the segments asthey move toward the bin 29 by, for example, providing means (not shown)for making turbulent the air through which they pass.

It is highly surprising that the individual resin-coated ends of the web15 break apart. Apparently it is necessary that each filament bundle orend be twisted about one or more turns per inch to realize goodseparation. Also, the fact that the resin is advanced to a tack-free andthus rather brittle state is an important factor in attainingseparation. When an identical web, except that the filament bundles haveonly one twist in 18 inches, is passed through the apparatus of FIGURE land coated with the same resin under the same conditions, the web doesnot separate completely and the action of the chopping device producesboards of a large number of resincoated ends. These boards have littleor no tendency to break into narrower segments, even when agitatedvigorously. Even at much lower density of filament bundles in the webduring coating, good separation does not result using the essentiallyuntwisted (one twist in 18 inches) glass.

In the apparatus of FIGURE 2, resin-coated fiber segments 28, such aswere produced as described above in connection with FIGURE l, aremetered out at a steady rate from a bin 30 to fall in a random mannerupon a belt 31. If the belt 31 is foraminous, means (not shown) may beprovided for blowing air downwardly through the belt to direct the fibersegments 28 to the belt and to assist in compacting the segments. Thedeposited fiber segments 28 are warmed, as by infrared lamps 32, to anextent sufficient to soften their resin coating, and are then drawnbetween a pair of rolls 33, preferably silicone rubber-coated, whichcompress the segments sufficiently to provide a handleable,shape-maintaining preformed sheet. The sheet may be cut to convenientlengths by means of a knife 34.

When heated to a temperature at which the resin coating has a viscosityin bulk in the range of about 50,000- 5,000,000 centipoises, thispreformed sheet becomes pliable and may be shaped to conform to complexsurfaces. It may then be molded under heat and pressure to produce adense, tough, monolithic molded object of high strength in threedimensions.

Complex preformed shapes, such as for the production of aircraftradomes, may be made from the resin-coated filament bundle segments 28of FIGURE 1 by means of conventional preforming apparatus and followingsteps similar to those described in conjunction with FIGURE 2. Preforrnsthus obtained need not be compressed, as by pressure rolls 33 beforebeing molded under heat and pressure, but need only be cooled to roomtemperature in order to be shape-maintaining and capable of withstandingordinary handling without injury.

Referring now to FIGURE 3, there is shown apparatus which demonstratesthe extraordinary owability of the novel molding compositions of thisinvention. Mounted centrally in a steel mold 40 of circularcross-section by means of a bolt 41 and torpedo 42 is a two-piecethreaded die 43. A cylindrical extension 44 of mold 40 is fitted with aram 45. The resin-coated fiber segments 28 of FIGURE l are placed in thehollow of extension 44, and the mold 40 and extension 44 are heated to atemperature such that the viscosity of the resin on fiber segments 28 isbrought within the range of 50,000-5,000,000 centipoises. Pressure isthen applied to ram 45, forcing the fiber segments 28 to flow throughthe narrow ring-shaped orifice 46 and into the cavity around the splitdie 43. If the quantity of fiber segments held by extension 44 isinsufiicient to fi-ll this cavity completely, it is necessary to removethe ram 45 to add another change of fiber segments. However, beforeadding the second charge, the uppermost segments of the previous chargeshould be loosened with a screw driver or other tool in order to effectintermingling of the filament bundles of successive charges.

After the molding composition completely fills the cavity around thethreaded die 43, the temperature may be raised to hasten curing of theresin. This substantially reduces the viscosity of the resin, wherebysome resin can fiow away from the fiber segments to form a flash atjoints 47 and 48.

When the resin is cured, the mold is taken apart and the reinforcedresin casting is saWed at the line of demarcation 49 between thethreaded die 43 and the torpedo 42, and eac-h half of the threaded dieis screwed out of the casting to provide a threaded pipe coupling ofexceedingly high strength. Surprisingly, it is found that the couplingis completely homogeneous, except that the crowns of the threads mayoccasionally be somewhat rich in resin. Y

Specific forms Iof this invention are illustrated by the followingexamples without intent to be limi-ted thereto.

Example 1 Spools of continuous glass filaments marketed by Owens-ComingFiberglas Co. under the designation ECG 150-1/0 5 end, treatment 038"were used in this example. These glass filaments Were initially providedwith a starch mineral oil iinish and eventually wound on rnetal spools.The glass while on the spools was heat-cleaned at a temperaturesufiicient to remove the finish, and while still soA wound was dipped ina solution to provide a size coating of gammaaminopropyltriethoxysilanein the amount of a small fraction of one per cent of the weight of theglass. Each end or bundle of filaments included 204 monofilaments ofabout 0.00038-inch diameter each.

The lglass filament bundles were fed from a large bank of spools throughan eyelet board and combs in single layer arrangement vand at a densityof ends per inch, as illustrated in FIGURE 1 of the drawing, and into abath of an epoxy resin condensation product of epichlorv hydrin andbisphenol A, having a softening point of about 45 C. as determined bythe Durrans Mercury Method,

and in admixture with a hardener consisting essentially of isophthalyldihydrazide. By immersion in the bath of resin, which was maintained atC. (at which temperature its viscosity was about 4000 centipoises), theglass filament bundles became a continuous resin-coated web which waspassed between a pair of heated steel rollers, the surface temperatureof which .was about 110 C. and the spacing between which was adjusted toprovide the web with a resin content of about 35 percent by weight.Since the specific gravity of the glass was 2.55 and that of the resinwas 1.18, the resin-filled web had a glasszresin volume ratio of about46:54. 'Dhe resin-coated web was cooled by passing it around a drum, thesurface temperature of which was held at about -10 C. As the resinhardened to a tack-free state, almost every individual resin-coated ends-pontaneously separated from adjacent ends. The web was then chopped toprovide a mass of resin-coated fiber segments one-half inch in length,which are useful as a reinforced-resin molding composition as describedbelow.

A quantity of this molding composition was placed in a closed press, theopening of which measured about 8 by 10 inches, the platens of whichwere preheated to about 165 C., and about 250 pounds per square inch ofpressure was applied. After 30 minutes at 165 C., the resinwas fullycured, and the resultant 1a-inch thick panel was immediately ejected.Specimens cut from the cured panel were tested in accordance withFederal Specification L-P-406b for ilexure strength (by Method 1031.1),for tensile strength (by Method 1011), and for compressive strength (byMethod 1021.1). The same procedure was followed using moldingeompositons identical except for length of the fiber segments. The dataobtained cornparing molding compositions of several segment lengths isrecorded in Table I. Each strength value is recorded in pounds persquare inch. Subsequent work with the same and similar compositionsindicates that the ilexure value for the 11A; inch iiber segments isabout 10% low.

TABLE I Segment length Flexure strength Tensile strength Compressive(inches) (p.s.i.) (p.s.i.) strength (p.s.i.)

Higher strengths are obtained if a long, narrow test panel is molded tosize and tested in the lengthwise direction instead of using specimenscut from an almost square panel as above, apparently due to the factthat the lilaments at the edge of the narrow panel are not cut.Resincoated fiber segments of identical composition were cured in a moldfor 30 minutes at 165 C. and at a pressure of 400 pounds per square inchto provide panels measuring 9 inches by l inch by 1A inch. The resultsobtained with these panels at various fiber-segment lengt-hs arerecorded in Table II, each value being the average of at least livespecimens. It will be noted from this table that rather high strengthsare achieved with -molding compositions of this example that usereinforcement about 3)@,2 inch in length, and through interpolation itwill be seen that molding compositions y using reinforcement 1%; inch inlength would give strengths approaching 50,000 pounds/ square inch.

' TABLE II Segment length (inches) Flexure strength Modulus in tlexure(p.s.i.) (p.s.i.

3e: 2s, 50o 3,000, 000 43, 500 2, 900, 000 71, 000 3, 200, 000 92, 0003, 600, 000

Y Other of the panels of l-inch segment length of Table II showed aflexure strength of 190,000 p.s.i. when tested at 60 C. and a Wetilexure strength at 24 C. of 78,000 p.s.i., when tested immediatelyafter removal from distilled water in which it was boiled for two hoursand then cooled.

To demonstrate the three-dimensional isotropy of the molded products ofthe composition of this example, 1/z-inch resin-coated ber segments wereplaced in a rectangular mold, 2 by 3 inches at the base and 6 inches inheight. The mold had been preheated to C. The molding composition wascompressed to three inches in height under a pressure of 1000 pounds persquare inch, after which the temperature of the mold was raised to C.and maintained for 45 minutes. Upon cooling, the molded block was sawedinto vertical and horizontal specimens of 1a-inch thickness, the blockhaving been compressed in the vertical direction. The specimens showed ahorizontal tensile strength of 26,000 pounds per square inch and avertical tensile strength of 8,730 pounds per square inch.

The test was repeated using one-inch liber segments of the same moldingcomposition. Horizontal tensile strength was 26,700 p.s.i. compared to5,000 p.s.i. vertically. Flexure strength of a horizontal specimen was47,400 p.s.i. and that of a vertical specimen was 13,600 p.s.i.

Because the fiber segments of the molded blocks were poorly interlockedin the vertical direction, the strengths reported for the verticaldirection are lower than can be expected in normal use. When using amold of limited height requiring compaction of the molding compositionbefore its introduction into the mold, care should be taken to insurerandom orientation of the fiber segments before such compaction, as bystirring or otherwise agitating the mass of segments-a precaution nottaken in molding the blocks on which the vertical and horizontal testswere made.

From the molding composition of this example in twoinch segment lengthwas molded an essentially square panel 1A; inch in thickness, withcuring for 30 minutes at 165 C. under 150 -p.s.i. The average flexurestrength of ten specimens cut from this panel was 80,800 p.s.i. Thecoefficient of variance in strength of the ten specimens was 7.7percent. Essentially identical results are attained with moldingcompositions prepared with glass filament bundles having one twist perinch and having a film-forming size including an adhesion-improvingagent. The presence of the film-former does not interfere with breakupinto small fiber segments of about one filament bundle each. However,when a web of essentially untwisted glass roving (one twist in 18inches) having a film-forming size and containing a chrome complexfinish to improve adherence of resin was passed through the resin bathof the example, the resin-coated web did not break up into small bundlesupon chopping to Z-inch lengths but formed board-like fiber segments.Most of these fiber segments were 1/32 to 1A; inch in width, i.e., about0.07 to 0.03 inch in circumference. The average flexural strength ofnine specimens cut from a panel made from this composition was only41,450 p.s.i. and the coefficient of variance in strength was 15.3percent.

The molding composition of this example, at 1/z-inch fiber segmentlength was used to fabricate a pipe coupling of 2-inch nominal diameterand having standard pipe threads, as illustrated in FIGURE 3 of thedrawing. With the mold preheated to 65 C. by means of metal platensmaintained at 175 C., a charge of the molding composition was forced ata pressure of about 200-500 pounds per square inch through thering-shaped orifice, which had a width of about V16 inch. Three chargesof the molding composition were required to iill the mold cavitycompletely. The pressure was then increased to 3000 p.s.i. After onehour the temperature of the mold had risen to about 140 C., at whichtime the mold was placed for an additional 2% hours in an aircirculating oven at an air temperature of C.

After quenching in water, the mold was taken apart and the moldedcoupling was sawed to release the torpedo and to allow removal of thesplit threaded die. The coupling was connected by its threads toapparatus exposing it to high internal hydrostatic pressures andwithstood 7500 p.s.i. without injury.

An identical coupling, except that the filament bundle segments were oneinch in length instead of one-half inch, burst upon exposure to 5700p.s.i. internal pressure. The best commercially-obtainable reinforcedresin pipe couplings of the same size usually fail at pressures below3500 p.s.i.

Example II A molding composition was made with the resin and by theprocedure of Example I but using fibrous glass marketed by Owens-CorningFiberglas as ECG 150 l/ 0 8 end, treatment 008. Each end or bundle offilaments includes 204 monofilaments of about 0.0003 8-inch diametereach. The glass filaments were produced in similar manner to theproduction of the glass filaments used in Example I, i.e., byheat-cleaning to remove the initiallyapplied starch mineral oil or otherfilm-forming finish in the size coating. The spool of glass filamentswas then sized by being dipped in a solution of methacrylatochromicchloride.

An essentially square panel, 1/8 inch in thickness, made from thismolding composition (with 1/z-inch filament bundle segment length) andcut to appropriate sizes for testing, yielded a flexure strength of54,300 p.s.i. and a tensile strength of 29,100 p.s.i. Conditions of curewere minutes at 165 C. under 150 p.s.i.

Example Ill A molding composition was made with the brous glass ofExample II and by the procedure of Example I but using a differentresin, i.e., a mixture of another epoxy resin with phthalic anhydride ashardening agent. The epoxy resin, specifically Epon 1310, as describedby the manufacturer, the Shell Chemical Corporation, as the condensationproduct of 1,1,2,2 tetrakis(4hydroxy phenyl) ethane and epichlorhydrinhaving about 3 glycidyl ether groups in the molecule. The substitutedethane is believed to be derived from glyoxal and phenol. Some of thephenyl groups may be substituted at the ortho rather than para positionwith respect to the ethane.

Using resin-coated bundle segments of 11/8 inches length, a 1As-inchthick panel was molded in a heated platen press at a temperature of 165C. and pressure of 150 p.s.i. for 30 minutes. Several specimens cut fromthis essentially square panel showed an average fiexure strength of65,000 p.s.i. and an average tensile strength of 32,000 p.s.i.

The molding composition of this example must be kept under refrigerationto remain useful for making molded products whereas the epoxy resincomposition of Example I employing a dihydrazide as the hardening agentremains stable for several months at ordinary room temperature. For usesnot entailing storage of the molding composition, it may be preferableto employ thermosetting resin compositions which cure more quickly thando the latent and semi-latent resins of the above examples.

Example IV The molding composition of Example I was compared toidentical molding compositions except that the monofilament diametersand number of filaments per bundle were changed. Each filament 'bundlehad a twist of one turn per inch. Panels 9 inches by 1 inch by 1/8 inchwere molded for 30 minutes `at 165 C. under 300 p.s.i. and tested toprovide the data reported in Table III, averaging 8 specimens for eachmolding composition.

TABLE III Filament No. filaments Fiber segment Flexure diameter perbundle length (inches) strength (psi.)

(inches) The data of Table III shows little change in strength withchange in filament diameter, the differences being within margins oferror. Since glass yarn having continuous filaments of greater averagediameter than 0.00053 inch is not commercially available, it was notpossible to test for maximum filament size, but it is neverthelessbelieved that filiments much larger than 0.0006 inch in diameter may betoo brittle for easy handling in the production of the novel moldingcomposition. A strand of 204 0.00053 inch diameter monofilaments has adiameter of somewhat more than 0.01 inch, and a strand of 204 0.0006inch diameter monofilaments -would be somewhat larger. On the otherhand, bundles `of glass monofilaments of less than about 0.0002 inchdiameter 'are considered too weak to handle in commercially-useful resincoating operations.

Example V A web of glass-filament lbundles as described in Example I`was passed under even tension through a bath of thermosettingphenol-formaldehyde resin. The resin had been prepared from 1,5 mols oflformaldehyde per mol of phenol, using about 0.5% by weight sodiumhydroxide as catalyst. A mixture of these ingredients had been reacteduntil the resin had a viscosity of about SOO-1000 centipoises at y" C.,whereupon the mixture was neutralized with an acid such :as citric acid.The resin had then been vacuum dehydrated to remove essentially allwater. With the web of glass moving at the rate of 6 inches per second,any point of the layer was immersed in the bath of resin which washeated to 80 C., for approximately 6 seconds. The resin-coated web wasthen drawn between calender rolls maintained at 80 C. and joined to acontinuous silicone-treated heat-resistant paper liner. The linercarried the web around a drum, the surface temperature of which was 175C., across Ian 8foot long plate heated to C., and then `across a 35-foot long plate, the surface of which was maintained at -18 C. Theupper surfaces of the two plates together formed a shallow invertedcatenary curve. The resin-coated web was wound together with the linerfor storage and later unwound and chopped into one-inch fiber segments.

Panels 9 inches 'by 1 inch by 1/s inch formed from this moldingcomposition at 165 C. for 30 minutes under 400 p.s.i. were tested atvarious temperatures after 30 minutes exposure to the test temperature.Average results of at least 3 specimens for each test temperature arerecorded in Table IV.

TABLE IV Temperature Flexure strength of test, C. (psi.)

24 92,000 93 40,500 149 33,000 205 33,000 260 24,000 The good retentionof strength at high temperatures by cured products of this moldingcomposition indicate it is especially fitted for uses in which exposureto heat might otherwise cause failure.

The brief heating to which the resin-coated web of this example wassubjected effected a partial curing or crosslinking of the resin suchthat upon subsequent further heating to temperatures preferred forcuring the resin, e.g. 165 C., the resin was highly viscous and soremained with and lubricated the fiber segments under molding pressure.This is in contrast to most thermosetting resins which become almostwater-thin upon initial heating to temperatures at which curing israpid, a characteristic which enables them to be used for impregnationof porous materials such as bundles of glass filaments without the useof solvents. The fact that the partially cured resin of the moldingcomposition of this example does not become free owing upon heatingmakes less critical the control of molding temperature. Because highertemperatures may be employed for molding, the molds are more quicklyavailable for reuse. Y

Epoxy lresin compositions such as those employed in the precedingexamples have likewise been partially cured by controlled heating, as inthis example, or by partial chemical reaction, e.g., by exposure toammonia gas, after being coated on a web of continuous glass filamentbundles and before chopping.

For certain uses such as for building preforms, lit is preferred thatthe fiber segments have a resin coating which .becomes highly tacky withmoderate heating so that each segment retains the attitude in |which itstrikes the preform screen. To have such property, partial curing isnorm-ally omitted, except that the resin may be partially cured afterthe preform is built and before it is pressed and fully cured.

Comparative example A web of lineally-aligned yarns of continuous glassfila- -ments having a vinyl-silane finish as described in U.S. Patent2,688,007 was coated with the resin and by the procedure of Example I.Each yarn, which had an approximate diameter of 0.025 inch, consisted offive interwoven pairs of intertwined bundles, with 204 filaments ofa'bout 0.00038-inch diameter in each bundle, viz., ECG 140-2/ 5 Garanfinish yarn of Owens-Corning Fiberglas Co. After application of theresin and upon chopping, the yarns readily separated into individualfiber segments of 0.025-inch diameter, comprising 50% resin by volume.

A panel 9 inches lby 1 inch by 1A; inch molded from one-inch fibersegments at 165 C. for 30 minutes under 500 p.s.i. exhibited a flexurestrength of 32,000 p.s.i. A11 identical panel formed from 1/z-inch fibersegments had a fiexure strength of 33,000 p.s.i. These values aresubstantially lower than those obtained with finer resincoated fibersegments and indicate the undesirability of utilizing fiberreinforcement of `0.025 inch diameter or of coated fiber segments muchgreater in circumference than 0.025 inch. This may be compared withExample IV where it was indicated that reinforcement of 204 0.0006 inchdiameter monofilaments give good results.

'I'he novel molding composition also may be formed using as the fibersof reinforcement bundles of continuous filaments of quartz-like glass,quartz and other glasslike continuous laments. The use of a singlefilament as a fiber of reinforcement instead of a group of hunchedmonofilaments is less desired, but single filaments of boron are usedwith good results, especially in specialized uses justifying boronsexpense. Carbon filaments such as those formed from cellulose fibersalso provide high-strength reinforcement, though they are presently lessstrong and more expensive than glass. A quartz-like glass yarn which canbe used to produce mold-ing compositions of superior [high temperatureresistance is produced by H. I. Thompson Fiber Glass Co. under the tradedesignation Refrasil. It is a leached-out glass containing more than 98%silica. Since its tensile strength is only about 25% that ofconventional glass, it is normally not applied to uses requiringparticularly high strength. Continuous quartz filaments, on the otherhand, are almost as strong as glass filaments and also lend superiorheat resistance to molded products of this invention. Accordingly, theterm glass filament is used generically to include such glass-likefilaments.

It should be -noted that mold release agents should be employed with themolding compositions of the above examples and with other moldingcompositions containing thermosetting resins. Thermoplastic resins canoften be used without mold release agents. However, thermosetting resinsare normally preferred in the practice of this invention because oftheir good adhesion to glass, resistance to heat, and other well-knownpoints of superiority as compared to thermoplastic resins. Athermoplastic resin which has been used to make molding compositions ofsome promise is high impact styrene, rubbermodified styrene. Since thisresin is conveniently coated from solution or dispersion, care must betaken to eliminate volatile vehicle before the composition is molded, orthe products will not be free from voids.

Additional components such as inert fillers or colored dyes or pigmentsmay be added in small amounts to provide a desired appearance, or toadjust the viscosity of the resin, or for other purposes, withoutmaterially changing the characteristics of the molding composition.

What is claimed is as follows:

1. The method 'of making a reinforced molding composition which flows ata useful molding temperature and molding pressure to occupy completely acomplex cavity as a continuous resin binder matrix filled essentiallyuniformly throughout with randomly intermingled fibrous reinforcement,and that then hardens as a monolithic object having high strengthproperties in all directions, said method comprising the steps of (l)arranging continuous yarns of glass monofilaments into a fiat compactsingle-layer web in which the yarns are in substantially parallelrelation, each yarn having (a) a diameter of no more than about 0.01inch, (b) a resin-receptive surface treatment, and (c) a twist of aboutone turn or more per inch; (2) drawing the web of yarns under eventension through a coating operation and coating the yarns with ahigh-strength strongly adherent liquid thermosetting organic resincomposition that is maintained during the coating operation within theviscosity range of 20G-12,000 centipoises; (3) bringing the resincomposition to a track-free brittle state in which the resin (a)comprises between about 35 and 60 percent of the total volume of eachresin-coated yarn, and (b) is highly Viscous at a useful moldingtemperature whereby the resin remains with and lubrcates the yarn onwhich it is coated during a molding operation; and (4) chopping the webof resin-coated yarns into individual resin-coated fiat fiber segmentsthat are each about 1A to 2 inches in length and consist of at least oneand no more than a few parallel adjacent yarns. 2. The method of makinga reinforced molding composition which fiows at a useful moldingtemperature and molding pressure to occupy completely a complex cavityas a continuous resin `binder matrix filled essentially uniformlythroughout with randomly intermingled fibrous reinforcement, and thatthen hardens as a monolithic object having high strength properties inall directions, said method comprising the steps of (1) arrangingcontinuous yarns of glass monolaments into a fiat compact single-layerweb in which the yarns are in substantially parallel relation, each yarnhaving (a) a diameter of -no more than about 0.01 inch, (b) aresin-receptive surface treatment, and (c) a twist of about one turn ormore per inch; (2) drawing the web of yarns runder even tension througha coating operation and coating and impregnating tthe yarns with ahigh-strength strongly adherent liquid thermosetting organic resincomposition; (3) bringing the resin composition to a tack-free brittlestate in which the resin (a) comprises between about 35 and 60 percentof dthe total volume of each resin-coated yarn, an (b) is highly viscousat a useful molding temperature whereby the resin remains with andlubricates the yarn on which it is coated during a molding operation;and (4) chopping the web of resin-coated yarns into in- -dividualresin-coated fiat fiber segments that are each about Ms to 2 inches inlength and consist of at least one and no more than a few paralleladjacent yarns.

3. A molding composition comprising a mass of monoyam -and multi-yarnber segments prepared by the method of claim 2.

4. The molding,7 composition of claim 3 in which the resin compositioncomprises a mixture of epoxy resin and 5 epoxy-reactive curing agent.

References Cited UNITED STATES PATENTS Swann 117-4 Baker 260-40Sonneborn et a1 164-61 Bradt 18--55 OTHER REFERENCES R. H. Sonneborn:Fiberglas Reinforced Plastics, Reinhold Pub. Co., New York (1954), pp.175-8() relied upon, coll No. TA455P55S6, copy in Gp. 140.

Anon: Chemical and Engineering News, Dec. 3, 1962, pp. 55 and 56 reliedupon.

MORRIS LIEBMAN, Primary Examiner.

I. E. CALLAGHAN, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington,D.C. 20231 UNITEDSTATES PATENT OFFICE CERTIFICATE QF CORRECTION Patent No. 3,403,069September 24, 196

Burton A. Benson It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected asshown below:

Column l, line 45, "exceeding" should read exceedingly line 52, m shouldread may Column 2, line 1l, "fo ruse" should read for use line 62,widely-space should read widely-spaced Column 7, line 30, "of" shouldread in Column l0, line 48, 0.03" should read .30 Column 13, line 36,"O. O25 should read 0. 05 Column 14, line 30, "track-free should readtack-free Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, Attesting OfficerCommissioner of Patents

